The general use of radiofrequency and high frequency generator systems which deliver electrical output to electrodes that are connected to a patient's body is known in the clinical literature and art.
By reference, an example of radiofrequency heat lesioning generators used in clinical practice for the treatment of neural disorders is the Radionics RFG-3C+ (Burlington Mass.).
This device is capable of delivering high frequency energy to patient tissue via an adapted electrode, and associated ground or reference electrode. This device is also capable of delivering low frequency stimulation pulses that are used to accurately localize the electrode placement before treatment.
Parameters that may be measured by these devices include impedance, HF voltage, HF current, HF power, and electrode tip temperature. Parameters that may be set by the user include time of energy delivery, desired electrode temperature, stimulation frequencies and durations, and level of stimulation output. In general, electrode temperature is a parameter that may be controlled by the regulation of high frequency output power.
These devices have various user interfaces that allow the selection of one or more of these treatment parameters, as well as various methods to display the parameters mentioned above.
In one application of these devices, a patient complains of back pain, or some other pain of nocioceptive or neuropathic origin. A doctor then performs diagnostic blocks with local anesthetic by injecting the anesthetic into the areas that is suspected of generating the pain. If the patient receives temporary relief from these injections the doctor concludes that the pain generators were in the location where he made these injections. Unfortunately, the origin of pain is poor understood; perceived pain at a certain level in the back, for instance, can actually be created from many different and multiple sources.
Once a location has been identified, the clinician will decide to deliver high frequency energy to this location to permanently destroy the pain generator. A ground or reference plate will be placed on the patient's thigh to provide a return path for the high frequency energy. An insulated electrode with a small un-insulated tip will be placed at the expected target. Stimulation pulses will be delivered at a sensory frequency (typically 50 Hz), and a stimulation voltage will be placed on the electrode. The clinician is looking for a very low threshold of response from the patient (e.g., less than 0.5 V) to ensure that the electrode is close to the sensory nerves. They will then perform a stimulation test at a muscle motor frequency (e.g., 2 Hz), and increase the stimulation voltage output to 2 v. In this instance, they are looking for no motor response in the patient's extremities as this would indicate the electrode was too close to the motor nerves. Treatment in this area could cause paralysis. Upon successful completion of these tests, high frequency energy is typically delivered for one or more minutes, while maintaining an electrode tip temperature between 70 and 90 degrees. Alternatively, high frequency energy may be delivered for one or more minutes, but in a pulsed mode where the high frequency energy is on for a short period of time and off for a long period of time, thus not producing any appreciable heating (reference is made to commonly assigned U.S. Pat. No. 6,161,048, the entire contents of which are specifically incorporated by reference herein).
Although these treatments are successful, they have several drawbacks. In practice, most patients need treatments at several different nerve locations. This requires placing the electrode, performing the stimulation, and delivering the energy at each location and then repeating the process, thus causing a great deal of wasted time, and patient discomfort, while waiting for the energy to be delivered. Another drawback is that in spite of successful stimulation testing, the target nerve is often not destroyed resulting in no decrease of pain. The clinician is left to determine whether the target nerve has been missed, or whether the pain generator is located else where in the body.